Erlangshan Mountain lies at the contiguous area of Tianquan county, Ya´an Prefecture, Sichuan Province and Luding County, Ganzi Zang Autonomous State. The Erlangshan mountainous area with complicated geology and dangerously steep mountains is characterized by harsh weather such as storm, heavy fog, snow, ice, strong wind and various frequently occuring natural disasters, such as landslide, rock falling and debris flow, and therefore the highway in this area is low in standard and poor in condition, resulting in serious traffic jam and frequent accidents, which threaten the safety of traffic. This paper describes the scheme study of disease countermeasures on the Erlangshan section of Sichuan - Tibet Highway and the project comparison of line alternatives, and presents the reasons of building a tunnel in the area, the tunnel alignment and the problems occurred in the construction. The dialectical relationships between a tunnel and its linking works, between a key project and an ordinary project are profoundly analyzed and the related experinences and lessons are also summarized, which will enlighten both the organizers and the designers on the construction of a project.